1. Field of the Invention
The present invention relates to a fired spinel complex oxide intending to recycle slag by-produced in chromium refining, and to a method for preparing the same. More specifically, the present invention relates to a fired spinel complex oxide from which alkaline components or chromium components do not leach and which is used for water-retentive and well-drained artificial aggregate, and to a method for preparing the same.
2. Description of the Related Art
For production of sodium chromate, in general, a mixture of chrome ore, soda ash, lime, and filler is oxidized and roasted at high temperature, and the roasted product is immersed in water to extract sodium chromate. Unfortunately, this process provides a large amount of leached residue.
The leached residue contains toxic hexavalent chromium, which pollutes soil and water to cause environmental deterioration if the residue is disposed of as it is. Therefore the residue is subjected to detoxification before disposal.
For example, Japanese Unexamined Patent Application Publication No. 48-32767 has disclosed the process of blending a residue of sodium chromate extraction with a reducer in an amount of 1 to 20 percent by weight to the residue and a material containing silica in a SiO2/CaO ratio of at least 1, and subsequently firing the mixture. For a residue of water extraction of chromates by-produced in sodium chromate and sodium dichromate production, Japanese Examined Patent Application Publication No. 47-35675 has disclosed the process of blending the residue with about 1 to 15 percent by weight of waste sulfuric acid containing oil, sulfate pitch, waste chlorinated hydrocarbon oil, or waste heavy oil. For chromium powder residue, Japanese Examined Patent Application publication No. 50-25915 has disclosed the process of roasting a mixture of the residue and activated carbon in a gas atmosphere with a low oxygen concentration at a temperature in the range of 400 to 1,000° C. and at a material temperature of 700° C. or less, and rapidly cooling it. Japanese Unexamined Patent Application Publication No. 47-23390 has disclosed the process of roasting a mixture of chromium powder slag, coke breeze, and powder clay at a temperature in the range of 1,000 to 1,300° C., and Japanese Unexamined Patent Application Publication 47-20089 has disclosed the process of roasting a mixture of chromium powder residue and activated carbon in a gas atmosphere with a low oxygen concentration at a temperature in the range of 400 to 1,000° C., and rapidly cooling it. Japanese Examined Patent Application Publication No. 50-25916 has disclosed the process of roasting a mixture of powder chromium slag, powder coke, and powder clay at a temperature in the range of 1,000 to 1,300° C. For a powder or granular slag produced in a sodium dichromate production, Japanese Examined Patent Application Publication No. 47-23319 has disclosed the process of blending or coating the slag with clay power and roasting the mixture or the coated material at a temperature in the range of 1,000 to 1,300° C.
In these processes, however, the detoxificated material is only disposed of, but not recycled.
One reason why the detoxificated material is not recycled is that it cannot ensure safety when recycled.
The inventors of the present invention have proposed the use of chromium slag in the field of ceramics in Japanese Unexamined Patent Application Publication Nos. 51-41009, 51-81806, and 59-92968.
The inventors have also proposed a fired spinel complex oxide (Japanese Unexamined Patent Application Publication No. 62-12661), a colorant for ceramics (Japanese Unexamined Patent Application Publication No. 62-36061, and another fired spinel complex oxide (Japanese Unexamined Patent Application Publication 3-205357) which are prepared from a chromium slag having a low calcium content and intend for recycling. The former fired spinel complex oxide is a reaction-sintered compact essentially composed of quartz and a solid solution spinel in which at least Al, Fe, and Cr interdiffuse, according to chemical composition analysis and X-ray diffraction analysis. This compact has a thermal conductivity of 1.3 to 2.5 kcal/mh° C. and a specific resistance of 102 to 107 Ωcm. The colorant is a chromium-containing iron composition containing as a principal constituent a solid solution spinel in which at least Fe and Cr interdiffuse, according to chemical composition analysis and X-ray diffraction analysis. The composition is fine powder having a Blaine specific surface of 2,000 to 5,000 cm2/g. The latter fired spinel complex oxide is a reaction-sintered compact of chromium slag powder and clay, essentially composed of quartz and a solid solution spinel in which at least Al, Fe, and Cr interdiffuse, according to chemical composition analysis and X-ray diffraction analysis. This compact has a thermal conductivity of 1.3 to 2.5 kcal/mh° C. and a specific resistance of 102 to 107 Ωcm.